Presents the. Rock Test Study Resource

Transcription

1 Presents the Rock Test Study Resource Created by Simone Markus Published by EngLinks 1

2 Preface This is a free resource provided by EngLinks for students in APSC 151. This presentation is a supplementary resource intended to compliment the course material not replace it. If there is discrepancy between this resource and the course material, the latter shall prevail. This resource does not cover all concepts taught in APSC 151 and thus should be used in combination with other study methods. Additionally some concepts in the following slides are not studied in the course and are only provided to assist students in gaining a more comprehensive understanding of the material. Choosing not to study these additional topics will not affect a student s success in the course. 2

3 Table of Contents Minerals... 4 Hardness Mohs Scale Hardness Useful Tools.. Cleavage Igneous 20 Sedimentary 27 Metamorphic 36 3

4 MINERALS The section aims to provide information needed to identify minerals taught in APSC 151. Slides 5 7 will focus on how two basic characteristics of minerals hardness and cleavage can be used in the identification process. Slides 8 19 outline characteristics of individual minerals, and attempt to provide tips on distinguishing them from those that are similar. NOTE: You will not be tested on material in these, and following slides, if it has not been taught in the course. 4

5 Hardness Mohs Scale Outline of the Mohs Hardness Scale The Mohs Scale places a number value on the hardness of materials. Minerals studied in APSC 151 have hardness values ranging from 2 (Gypsum) to 7 (Quartz). To help in the identification of minerals, objects such as finger nails, copper pennies, glass plates and knives can be used (see next slide). 2. Gypsum 2.5. Finger Nail 3. Calcite, Copper Penny Minerals are scratched by objects harder than them, and will in turn scratch softer objects. This is a useful tool for making the distinction between minerals of similar appearance. For example gypsum can be scratched by a finger nail while calcite cannot. An important note is that a mineral with a similar hardness to an object may or may not scratch it, for example feldspar, which has a similar hardness to a knife. 5 6 (range) Plagioclase and Potassium Feldspar, Glass plate, knife 7. Quartz 5

6 Hardness Useful Tools Though unconventional, a penny can be used to determine mineral hardness. Example: calcite will scratch a penny, while softer minerals will not. Knives can be used to scratch minerals and test their hardness. Note: the Mohs hardness of different knives may vary. Different minerals will leave different colour powder (streaks) on streak plates. Hard minerals such as Fingernails can be used to quartz, olivine and test hardness for softer garnet will scratch glass minerals. Minerals such as gypsum and chlorite may be scratched, while harder minerals will not. 6

7 Cleavage Cleavage is the tendency of a mineral to break along a planar surface. In other words; cleavage affects the shape of the minerals, and angles between faces can be used as an identification tool. Cleavage can occur in up to 3 dimension, thus minerals may have 0 (Quartz), 1 (Mica), 2 (pyroxene), or 3 (calcite) cleavages. Example: Cleavage is useful in identifying pyroxene (which has 2 cleavages at ~ 87 o and 93 o) from amphibole (2 cleavages at ~120 o and 60 o ). NOTE: Not all cleavage planes are perfect, and it is sometimes difficult to determine cleavage of some samples. Minerals may fracture along planes that are not aligned with cleavage. Additionally certain minerals are classified as having better cleavage than others. For example cleavage is excellent in calcite but poor in olivine. Pyroxene ~90 o Pyroxene Indistinct Cleavage ~60 o Amphibole 7

8 Quartz Cleavage: None Colour: Variety (151 samples often colourless) Lustre: Vitreous (greasy) Hexagonal crystals Hardness: 7 Will scratch glass Differences from similar rocks and minerals Quartzite: Quartzite is a metamorphic rock made of quartz, it contains many quartz crystals which are generally more intergrown than crystals found in Quartz Calcite: Calcite has defined cleavage while quartz does not. Quartz will scratch glass while calcite will not. Quartzite 8

9 Potassium Feldspar Cleavage: 2 cleavages at ~90 o Colour: Pink to red, grey white Streak: White Hardness: 6 May or may not scratch glass. Will scratch penny. Differences from similar minerals Plagioclase: Pink colour, no striations 9

10 Plagioclase Feldspar Cleavage: 2 cleavages at ~90 o Colour: white to grey, greenish or pinkish Streak: White Striations (lines on mineral face) Hardness: 6 May or may not scratch glass. Will scratch penny. Differences from similar minerals Potassium Feldspar: Colour, presence of striations 10

11 Muscovite Mica Cleavage: Basal (sheetlike) Colour: colourless to pale green/yellow Biotite Mica Cleavage: Basal (sheetlike) Colour: dark brown to black 11

12 Calcite Cleavage: Rhombohedral Colour: Usually colourless to white, but may be tinted Hardness: Scratched by knife, will scratch penny. Differences from similar minerals/rocks Gypsum: Calcite will scratch a penny, gypsum will not Plagioclase: Calcite is much softer and will be readily scratched with a knife. Calcite also lacks striations 12

13 Amphibole Pyroxene Amphibole Amphibole Pyroxene Pyroxene Cleavage: 2 cleavages at ~90 o Colour: Light to dark green Streak: White to grey Differences Amphibole Cleavage: 2 cleavages, at ~124 o and 56 o Colour :Black to greenish black Streak: white to greenish grey Elongated crystals Pyroxene Hardness: 6 May or may not scratch glass. Will scratch penny For differences between amphibole/pyroxene and dark coloured rocks, see slides in the igneous and metamorphic sections. 13

14 Pyrite Chalcopyrite Chalcopyrite Pyrite Cleavage: Poor Colour: Opaque dark yellow Streak: Greenish black Pyrite appears more metallic Chalcopyrite Cleavage: Poor Colour: Dark or brassy yellow Streak: Greenish black Hardness: Will probably scratch glass Pyrite is much harder than chalcopyrite Hardness: Will scratch penny Pyrite Pyrite Note: Pyrite crystals can appear in cubes Pyrite Chalcopyrite 14

15 Sugar-like crystals Olivine Cleavage: Poor, in 2 directions at 90 o Colour: Pale green to yellow-brown-green Streak: white to yellow-ish Hardness: 6.5 Will scratch glass Differences from similar minerals Pyroxene: Olivine has sugary crystals and is generally a lighter shade of green than (greenish) pyroxene. 15

16 Galena Cleavage: Nearly cubic Colour: Silver-metallic grey Streak: grey Hardness: Galena has a high specific gravity (it will feel heavy for it s size!) 16

17 Chlorite Cleavage: 1 cleavage plane Colour: Green to dark green Streak: White to pale green Hardness: 2 Scratched by fingernail Differences from similar rocks Garnet-Chlorite-Biotite Schist: Schists are rocks of metamorphic grade. Due to this they are deformed and minerals may be elongated. If trying to distinguish between the two, look for other minerals in the rock (garnet and biotite). 17

18 Garnet Cleavage: None Colour: Varies (often dark red, red brown, green or pink) Twelve sided crystals common Hardness: Will scratch glass 18

19 Strongly magnetic! Magnetite Colour: Black or grey-black Streak: Dark grey Hardness

20 IGNEOUS In APSC 151 igneous rocks are classified on rate of cooling (grain size) and composition. The table below shows an outline of where the studied rocks fall on this spectrum. Note: Pumice is not shown below, however it will be discussed in following slides. Felsic Intermediate Mafic Intrusive Slow cooling (coarse grained) Pink Granite Granodiorite Gabbro Granite Porphyry White Granite Extrusive Fast Cooling (fine grained) Rhyolite Andesite Basalt Amygdaloidal Basalt 20

21 Igneous Rocks: Felsic Intrusive (Granite) Felsic rocks are typically composed of feldspar, quartz, (light minerals) mica and amphibole (dark minerals). The felsic igneous rocks displayed below and on the next slide were cooled slowly during formation, allowing for the development of larger mineral crystals. Pink Granite White Granite Though there is an obvious difference in colour, pink and white granite have similar compositions. The difference in colour is due to variation in the types of feldspar present. Rocks classified as pink granite generally contain more potassium feldspar, and white granite contains more plagioclase. 21

22 Igneous Rocks: Felsic Intermediate Intrusive Granite Porphyry Granite porphyry contains crystals with distinctly difference sizes. To distinguish granite porphyry from other igneous rocks, look for a felsic coarse grained rock with one (or more) set(s) of crystals larger than the others. Granodiorite is an intermediate intrusive igneous rock. The composition of this rock is similar to granite, however it contains significantly more plagioclase than potassium feldspar and less quartz. 22 Granodiorite

23 Igneous Rocks: Felsic Extrusive Rhyolite is a felsic extrusive rock with a similar composition to granite. The visual difference between rhyolite and granite is the grain size. Rhyolite may be confused with quartz sandstone, however sandstone will generally feel more rough and have grains visible to the naked eye. Rhyolite 23

24 Igneous Rocks: Intermediate Extrusive Andesite is an intermediate extrusive igneous rock. Samples is APSC 151 have a porphyritic texture which they can be identified by (see granite porphyry slide for description of this texture). The larger crystals in andesite are generally dark minerals such as amphibole and pyroxene. Andesite Porphyritic Texture Amphibole (large crystals) 24

25 Igneous Rocks: Mafic Mafic Igneous rocks appear darker in colour due to the presence of minerals such as amphibole, pyroxene, olivine and biotite. Gabbro and basalt have similar compositions, but gabbro is intrusive (coarse grained) and basalt is extrusive (fine grained). This makes it easy to tell the two apart. Amygdaloidal basalt is simply basalt containing amygdules. Amygdules are gas bubbles or vesicles filled with secondary minerals (calcite, quartz, chlorite, etc.). Due to their dark colour, igneous mafic rocks are often confused with other dark rocks and minerals. To distinguish between basalt and amphibole, look at the cleavage. Amphibole as mentioned has cleavages at ~120 o and 60 o. For comparison to dark metamorphic rocks (see later slides), look at mineral assemblage and shape. Individual metamorphic rocks have defined compositions that vary from basalt/gabbro, looking for specific minerals helps to tell these rocks apart (discussed later). Gabbro Basalt Amygdaloidal basalt 25

26 Pumice Pumice is formed from explosive volcanic eruptions. It is extremely porous and has a very low specific gravity. Pumice is felsic in composition. 26

27 SEDIMENTARY Sedimentary rocks form from the deposition of material on the earths surface and within bodies of water. Grain size in sedimentary rocks is based on depositional environment. Coarse grained rocks are generally formed in high energy environments, while fine grained rocks (including evaporites) are formed in low energy. Clastic Chemical Greywacke Conglomerate Shale Quartz Sandstone Fossilferous Limestone Gypsum Potash Chert Rock salt 27

28 Beds Quartz Sandstone Quartz sandstone is a sedimentary rock composed of sand grains (typically between mm and 2 mm in diameter). It can often show bedding (displayed above). The samples in APSC 151 generally show bedding that is red to brown in colour. 28

29 Greywacke Rocks classified as greywacke can have varying compositions. It is also often referred to as a dirty sandstone. Greywacke has a greater range of grain sizes than quartz sandstone. It can be assembled of quartz, feldspars and varying amounts of other minerals. Greywacke can be distinguished from conglomerate on the basis of clast shape and size (the term clast refers to the grains that are distinctly larger than others). The clasts in conglomerate are round as opposed to angular and often large in relation to those in greywacke. 29

30 Conglomerate Conglomerates are sedimentary rocks consisting of clasts (larger than 2 mm) which are contained between grains of smaller size (also called a matrix ). Conglomerate clasts are defined as being rounded. Conglomerates are generally formed in a high energy environment (reason for large grain size). Rounded clast 30

31 Fossilferous Limestone Fossils Limestone is a sedimentary rock formed through biological and chemical processes. The prefix fossilferous is used to indicate a fossil bearing limestone. Limestone generally appears grey, however in some cases (see below) it may be darker. Fossils Limestone of dark grey black colour can also occur. This rock may or may not contain fossils. 31

32 Evaporites Formed through processes of evaporation, these sediments are generally soft (hardness ~2-3). They are relatively easy to distinguish from other chemical sediments such as chert and limestone. (Note: Chert can be formed in a variety of ways, and thus is not presented on this Gypsum White slide.) Rock Salt (Halite) Composed of NaCl tastes salty (EngLinks does not officially condone licking rocks) Generally clear to white to grey colour Potash Contains potassium (note: pink colour) Much softer than similar looking potassium feldspar 32

33 Chert Composed of quartz (will scratch glass) Forms in a variety of ways (chemical and biochemical) Colour varies Smooth along fractures 33

34 Shale Shale, sometimes referred to as mudstone, forms in a low energy depositional environment. It is platy and generally grey black in colour, though it may have a brown or green tinge. A common issue in APSC 151 is distinguishing shale from slate. Slate is a metamorphosed shale and thus they have similar compositions and appearances. The next slide goes over the differences between these two rocks. 34

35 May feel smoother than shale Shale vs. Slate Shale Beds can be slightly wavy and are generally rough Slate Generally appears more flat 35

36 METAMORPHIC The information below (also found in the APSC 151 lab manual) outlines the formation of various metamorphic rocks. See the following slides for in-depth descriptions of the listed metamorphic rocks (bolded). Note: As slate was discussed on the previous slide, it is not further discussed here. Shale (sedimentary) Slate Muscovite Schist Quartzofeldspathic Gneiss Migmatite Basalt/Gabbro (igneous) Chlorite Schist Amphibolite Gneiss Granite (igneous) Granite Gneiss Quartz Sandstone (sedimentary) Quartzite Limestone (Sedimentary) Marble 36

37 Marble Marble is a non- foliated metamorphic rock. Marble forms when limestone (composed of calcite) undergoes metamorphism. Marble and quartzite (next slide) can sometimes be confused for igneous rocks. However igneous rocks are formed from the cooling of magma. They therefore are composed of more than one primary mineral, while marble and quartzite are mainly composed of calcite and quartz, respectively. Recall that calcite has a hardness of 3 and therefore will not scratch glass, while quartzite will. 37

38 Quartzite. Quartzite is a hard, non foliated metamorphic rock generally formed from quartz sandstone. When the sandstone is cemented, quartz recrystallizes into interlocking crystals contributing to it s glassy appearance. How to distinguish from marble: Quartzite is very hard and will scratch glass How to distinguish from quartz: In un-metamorphosed quartz crystal shape is more distinct. 38

39 Schists Schists are medium grade metamorphic rocks. They contain a large portion of platy and elongated minerals. The schists studied in APSC 151 are named for the minerals they contain. Though it is not essential to memorize the nomenclature for metamorphic rocks the mineral listed closest to the rock type (in this case schist) is the most abundant. For example in a quartz-garnet-muscovite schist, muscovite is most abundant. Quartz-Garnet-Muscovite Schist Muscovite gives this rock its shiny lustre. Garnet crystal. Recall: garnet will scratch glass. 39

40 Schists Chlorite can gives a slight green colour Garnet-Chlorite-Biotite Schist Biotite may give this rock a shiny lustre. Garnet crystal. Recall: garnet will scratch glass. 40

41 Schists This schist, composed of biotite has a shiny lustre. It can be distinguished from un-metamorphosed biotite mica by it s degree of alteration. Biotite Schist 41

42 Gneisses Gneiss is formed by high grade metamorphic processes. Gneisses can be distinguished from schists (and other less metamorphosed or non metamorphosed rocks) by their degree of alteration. They are often foliated (composed of layers of sheet-like planar structures), which are referred to as gneissic bands. Granite Gneiss Pink Granite Metamorphism (notice the change) 42

43 Quartzofeldspathic Gneiss Gneisses Quartzofeldspathic Gneiss is distinctive due to it s highly developed bands. Though it can appear similar to granite gneiss, it s foliation is more developed. 43

44 Amphibolite Gneiss Amphibolite Gneiss is a metamorphic rock composed mainly of amphibole. Gneisses Amphibole and other minerals in this rock are altered and elongated, distinguishing amphibolite gneiss from other dark coloured rocks (specifically amygdaloidal basalt) Note the presence of small amounts of other minerals, also distinguishing amphibolite gneiss from other dark coloured rocks. Note: Though the grains in this rock may display typical amphibole cleavage, the 44 rock as a whole will not.